Generally, MIMO (multiple input multiple output) scheme means the scheme of increasing system capacity in a manner that a base station or a mobile station simultaneously transmits several data streams (or layers) spatially using at least two transmitting/receiving antennas. The MIMO scheme includes transmit diversity, spatial multiplexing or beamforming.
In the transmit diversity scheme, the same data information is transmitted via several transmitting antennas, thereby implementing highly reliable data transmission advantageously without channel related feedback information from a receiver. The beamforming is used to increase a reception SINR (signal to interference plus noise ratio) of a receiver in a manner of multiplying each transmitting antenna by an appropriate weight. In the beamforming, since uplink/downlink channel is generally independent in FDD (frequency division duplexing) system, highly reliable channel information necessary to acquire an appropriate beamforming gain. Hence, the beamforming receives a separate feedback from a receiver and then uses the received separate feedback.
The spatial multiplexing scheme may be categorized into a single user spatial multiplexing scheme and a multi-user spatial multiplexing scheme. The single user spatial multiplexing scheme is called SM (spatial multiplexing) or SU-MIMO (single user MIMO). According to the spatial multiplexing scheme, a plurality of antenna resources of a base station are entirely allocated to a single user (or mobile station) and capacity of MIMO channel increases in proportion to the number of antennas. Meanwhile, the multi-user spatial multiplexing scheme is called SDMA (spatial divisional multiple access) or MU-MIMO (multi-user MIMO). According to the multi-user spatial multiplexing scheme, a plurality of antenna resources or radio space resources of a base station are distributed to multiple users (mobile stations).
In case of using the MIMO scheme, there are a single codeword (SCW) method of transmitting N simultaneously-transmitted data streams (or layers) using a single channel encoding block and a multiple codeword (MCW) method of transmitting N data streams using M channel encoding blocks (M≦N). In this case, each of the channel encoding blocks creates an independent codeword (CW) and each codeword is designed to enable independent error detection.
Machine-to-machine (hereinafter abbreviated M2M) communication literally means a communication between one electronic device and another electronic device. In a broad sense, M2M communication may mean a wire/wireless communication between electronic devices or a communication between a human-controllable device and a machine. Recently, the M2M communication generally indicates a communication between electronic devices, i.e., a device-to-device wireless communication performed without human involvement.
In the early 1990's, in which the concept of the M2M communication has been initially introduced, the M2M communication has been recognized as remote control or telematics or the like and derivative markets of the M2M communication were very limitative. Yet, the M2M communication has grown rapidly for past few years and has become the globally noteworthy markets. Specifically, in POS (point of sales) and security related application markets, the M2M communication has considerably influence on such field as fleet management, remote monitoring of machinery and equipment, smart meter for auto-measurement of operating time, consumed heat or electricity quantity on construction machinery equipment and the like. M2M communication in the future will be further utilized for various usages in connection with a small-scale output communication solution such as conventional mobile communication, wireless high-speed interne, Wi-Fi, ZigBee and the like and may lay the foundation of expansion to B2C (business to consumer) markets instead of being confined to B2B (business to business) markets.
In the era of M2M communication, every machine equipped with SIM (subscriber identify module) card enables data transmission and reception and is capable of remote management and control. For instance, as M2M communication technology is usable for numerous devices and equipment including vehicles, trucks, containers, autovending machines, gas tanks and the like, its application fields may reach far and wide.
According to a related art, since mobile stations are managed by individual unit in general, a communication between a base station and a mobile station is usually performed by a one-to-one communication scheme. Assuming that numerous M2M devices communicate with a base station by the one-to-one communication scheme, network may be overloaded due to the occurrence of signaling between the base station and each of the numerous M2M devices.